The MEI Low Side Large Tracer Stick Capsule 8463EA is injected into the a/c system through the low pressure valve. The a/c system is then operated to thoroughly circulate the dye in the system. When the refrigerant escapes from the system, it will leave a residual amount of dye at the point of leakage. The ultraviolet light will then locate the point of leakage revealed by a bright fluorescent glow.